I've never heard of a 3 year distemper b/c all distemper vaccines should last at least that long. It's probably just a regular one labeled that way.
Or is it recombinant?
This is exactly why I stopped titering. Ellie's distemper came back low twice for no reason. Decided it was a waste of money. You are in more of a spot though. Absolutely ridiculous that they wouldn't get a single in for you. I'd call around again if you want it. Ellie's vet automatically did it for me. They aren't hard to get, it's just that vets don't want the rest of the box sitting around for just one dog.
The rest is JMHO. I would do DHPP again for Lane. She is so young still and I'd be concerned that the titer is actually alerting you to something important. Remember also that dogs can be non-responders, but I doubt that would be the problem here. I would not revaccinated Rory, but because you ahve to I guess you have to. I would do distemper only in that situation. I would not give it yearly though; so if this keeps happening, something else would need to be figured out. Talk to the vet about the 3 year distemper. See what company it is, etc. If she thinks that the daycares will take that instead of titers, it would be a definite consideration.